CBQE-545: Correction in xdcr automation

- swap_rebalance_out_master
  new master to be the node that was swapped in for
  the older master

Change-Id: I88e4c12fe271b79c561f2e74d0045b5524f698c2
Reviewed-on: http://review.couchbase.org/24317
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: abhinav dangeti <abhinav.dangeti@gmail.com>